This invention relates to vehicle suspensions for free rolling (i.e. non-driving axles) and has particular application to suspensions used with minimum width axles arranged in clusters of multiple axles having two or more axle assemblies mounted laterally opposed to each other across the width of the vehicle and one or more lines of axles mounted along the length of the vehicle, such is commonly employed on a trailer.
Suspensions of this type utilize air springs to support the load with pneumatic pressure. The air springs also deflect to absorb bumps and uneven road surfaces. The air springs are commonly interconnected for groups of axles with pneumatic hoses or pipes to provide equal pressure to groups of axles so that each axle within a connected group carries a relatively equal portion of the total load. This suspension is commonly referred to as a “trunnion axle suspension” meaning the axle is mounted on a swivel joint or trunnion that permits the axle to rock upwardly and downwardly relative to its longitudinal axis. This upward and downward motion is necessary to maintain ground contact and equal wheel loading for the wheels on both ends of each axle.
Lateral forces imposed on these types of axles are significant and they are caused by centrifugal turning forces, the lateral component of gravitational forces when the vehicle is on banked surfaces and most significantly, the lateral wheel skid force created when the cluster of axles is forced to turn. During turning the forward axles in the cluster must skid toward the inside of the turn while the rear axles skid toward the outside of the turn. This is known as “skid steer” force which is relatively high due to the coefficient of friction of the tires gripping the road and irregularities such as ruts in the road's surface.
In the prior art these lateral forces are resisted by a combination of the front suspension arm pivot bearing and a rear mounted sliding guide bearing that checks lateral movement of the suspension arm while permitting rotation of the arm about its pivot axis adjacent the frame. An example of such a system can be found in U.S. Pat. No. 6,286,857 to Fontaine et al. Fontaine employs a “cage” attached to the frame and sized to surround a bumper on the trailing portion of the trailing beam to prevent movement of the trailing beam horizontally transverse to the direction of vehicle travel while permitting movement of the trailing portion vertically.
It is common practice for these types of suspensions to use elastomer bearings at the points of articulation. These elastomer bearings absorb movement within the elastomer material (commonly a resiliently deformable material such as rubber) by its internal deflection. This eliminates surface against surface movement within the bearings and the wear associated with it. These elastomer bearings feature relatively long life and low maintenance (no lubrication is required) as the wear factor is virtually eliminated. Elastomer bearings, depending on their design, with allow a certain amount of axial misalignment, radial offset and axial offset as the elastomer deflects under load.
The sliding guide used in the prior art involves sliding surfaces and is prone to wear. This wear causes the guide clearance to increase over time and thus compromises suspension and axle alignment. There are also significant maintenance requirements required for this type of bearing. Other common methods have been employed to resist lateral forces such as rear mounted control rods, commonly known as “Panhard Rods”. These rods are control rods mounted in a lateral orientation, having spherical or elastomeric joints at their ends. One end is anchored to the chassis while the other is anchored to the axle or suspension trailing arm. As the axle or trailing arm moves vertically, the end of the Panhard Rod attached to it will follow an arc path. Although the axle cannot move freely in a lateral direction, it is forced to move laterally a small amount due to the radial offset of the arc. This will cause misalignment of the axle as the suspension ride height changes. The use of a Panhard Rod can lead to greater suspension cost and maintenance and to increased tire wear.
Consequently, there is a need for a trunnion axle suspension system which eliminates the requirement for a mechanism which resists lateral forces on the arm, other than at the pivot axis of the trailing arm. This has the advantage of resisting lateral movement of the axle (that is rotation about a vertical axis and/or axial movement along the pivot axis) with respect to the frame in a controlled manner by means of resiliently deformable bearing members at the pivot axis only. This overcomes the problems associated with resisting or controlling this lateral movement of the trailing arm at a position remote of the pivot axis, where upward and downward motion of the trailing arm with respect to the frame occurs.